Inside an ideal, long solenoid, the magnetic field is uniform in magnitude and parallel to the axis.

The magnetic field strength $B$ is directly proportional to current $I$ and turns per unit length $n$.

The external magnetic field of a long solenoid is extremely weak and assumed to be nearly zero.

A current-carrying solenoid behaves remarkably similar to a standard bar magnet with distinct North and South poles.

Provides a controllable, strong, and highly uniform magnetic field inside its core.

The magnetic field strength and polarity can be easily altered by changing the current magnitude or direction.

Generates heat ($I^2 R$ losses) due to current flowing through resistive wire turns.

Field uniformity drops significantly near the open ends and edges of short solenoids.

Used as electromagnets in inductors, relays, electrical valves, and switches.

Core component in Magnetic Resonance Imaging (MRI) machines to produce strong uniform fields.

Permeability of free space constant: $\mu_0 = 4\pi \times 10^{-7} \text{ T}\cdot\text{m/A}$.

Option B is wrong because $B$ is directly proportional to current ($B \propto I$), not inversely proportional.

Option C is wrong because the magnetic field is zero outside, but strong and uniform inside.

Option D is wrong because the field inside is uniform everywhere and actually drops to half at the extreme edges.